1. Field of the Invention
The present invention generally relates to an apparatus for storing data. More particularly, the present invention is directed to one or more storage units and a detachable assembly thereof. Each storage unit has a storage medium support structure which is configured to movably support at least one storage medium carrying member.
2. Discussion of Background Information
It has been recognized that rewritable optical disks are subject to less stringent environmental restrictions than magnetic disks. This is because in order to achieve greater densities in magnetic disk storage devices, read/write heads generally need to be positioned extremely close to the media surface of the magnetic disk or platter. As a practical matter, the read/write head may be placed so close to the surface of the platter that it is spaced from the surface only by the rush of air between the arm holding the head and the media surface. The tolerances for the distance between the head and the media surface are extremely stringent--so stringent that the presence of dust particles or other contaminants can significantly affect the operation of the read/write head. Thus, an entire magnetic disk storage device, including all platters and read/write units, must be enclosed in a "clean", i.e., completely sealed, environment which cannot be opened without introducing damaging and sometimes fatal contaminating materials, such as dust particles, to the recording media on the platters. As a result, if there is a failure in the recording media and/or in the read/write units of a magnetic disk storage device, repair requires the complete replacement of both the recording media (i.e., all of the platters) and the read/write units.
One of the most common problems occurring with magnetic disk storage devices involves a phenomenon known as a "head crash." During a head crash, a read/write unit of a magnetic disk contacts the recording media-of an associated platter. Such contact typically may result in permanent damage to the platter surface, may result in loss of data, and may even render the platter unusable. Because the complete device, including all platters and their associated read/write units, is sealed, the complete device must be removed and replaced as a single entity. Such a replacement may take a significant amount of time, such as, several hours.
In addition, once the storage device is replaced, the original contents, which are usually stored in archival storage devices, must be reloaded into the new magnetic disk storage device, and any subsequent updates after the archival dates must be recreated. Depending on the size of the storage device being reloaded, this reloading process can take a substantial amount of time.
Optical disk storage devices do not have many of the disadvantages associated with magnetic storage devices, such as the "head crash" noted above. Platters in an optical disk storage device typically are located relatively far away from their associated laser read/write heads, as compared to the magnetic disk storage device. For example, a read/write head may be positioned about 3 mm away from the surface media of a platter. Thus, dirt, dust, and other small particles will not likely affect the reliability of the optical storage device. Moreover, since the read/write head is not close to the surface media, head crashes rarely occur. Failures in optical disk storage devices are usually limited to: (1) failure of actuator assemblies or axle motors; and (2) failure of the system controller which supervises actuator and optical head positioning and data transfer to and from disks.
Another problem associated with magnetic disk storage devices (and other magnetic storage devices) is that they take up a significantly larger amount of space, as compared to optical storage devices. Thus, optical storage devices may be used in order to reduce the amount of space needed to store data.
Because of the limitations associated with magnetic storage devices, which have been predominantly used for storing data for digital computer systems, many data storage systems are inflexible and quite costly. For example, since during manufacture, the magnetic storage disk device must be preassembled in a "clean room" free from any stray particles, debris, and dust, standard fixed-size magnetic disk storage devices must normally be purchased. Thus, if a storage device is purchased which is larger than needed, excess space is wasted and an unnecessary expenditure is incurred. On the other hand, if a relatively small magnetic storage device is purchased, and in a short time a larger magnetic storage device is required, two or more magnetic storage devices must be combined (which may have a negative effect on the speed of the system, or require additional hardware to interact with the magnetic storage devices), or a larger magnetic storage device must be purchased.
It is thus desirable to provide a storage device which occupies a relatively small amount of space, has a high storage capacity, can be easily reconfigured to allow storage of more or less data depending on the present needs of the system to which the storage device is connected, and may be easily repaired without replacing the entire storage device.
U.S. Pat. No. 4,888,751 (YOSHIMARU et al.) discloses an image information processing apparatus which may accommodate a number of optical disks, and which is capable of supporting up to five optical disks. The apparatus disclosed by YOSHIMARU et al., however, has a fixed outer dimension. That is, the overall frame structure of the storage device has a fixed size, and if less than five disks are loaded, spacers or collars must be used to occupy the extras space not being used. Thus, when one is using less than five disks, the same overall storage space (dictated by the dimensions of the outer frame structure of the storage device), is still occupied. When one wants to expand the potential storage capacity of the overall unit, there is a fixed maximum number of disks (e.g., 5) which may be accommodated. Additionally, since each of the elements of the apparatus disclosed by YOSHIMARU et al. are relatively permanently secured to each other, it is difficult to disassemble the apparatus of YOSHIMARU et al., thus inhibiting repair of, and access to, elements of the apparatus.